spinewidth not accepted in GeoAxis

[filchristou]

It looks spinewidth is not supported for a GeoAxis

let
	fig = Figure()
	ax = GeoAxis(fig[1,1], spinewidth=10)
	fig
end

Are there any work-arounds ?

[filchristou]

Probably related to #195

[filchristou]

I ended up doing a black poly around the axis limits. The result is pretty good but requires extra effort.